A problem concerned with power tools of this type is the considerable exhaust noise from the motor. This is particularly annoying at idle running when no process noise is created. For instance in pneumatic grinders the process noise created during grinding is very loud and dominates completely over the exhaust noise from the motor, which means that even during operation when the motor is delivering full power the exhaust noise from the motor is no problem. When, however, the motor is relieved from load the speed governor will automatically start choking the pressure air inlet flow so as to bring down the power output of the motor and hence limit the idle speed of the motor. Still there is a considerable noise emanating from the motor exhaust, and since there is no process noise present the motor exhaust noise will be dominant and cause an annoying noise level at the working site.